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2.3 Sex-Influenced Traits, Dosage Compensation & Barr Body — Test 1
Q1. When autosomal genes are more readily expressed in one sex than the other, this is known as a:✓ Sex-influenced trait
Q2. Which of the following is a sex-influenced trait?✓ Pattern baldness
Q3. Male-limited precocious puberty is an example of:✓ Sex-limited characteristic
Q4. Genes for a trait that are inherited by both sexes but manifest a phenotype only in women are called:✓ Sex-limited
Q5. Dosage compensation in mammals is achieved by:✓ Heterochromatinisation of one X chromosome in females
Q6. The commonly observed dosage-compensation mechanism in mammalian females involves:✓ Inactivation (methylation) of one X chromosome
Q7. Dosage compensation in Drosophila is characterised by:✓ Hyperactivation (up-regulation) of the single X in males
Q8. In mammals and Drosophila, sex determination and dosage compensation differ as:✓ Y presence + X inactivation (mammals); X:A ratio + X hyperactivation in males (Drosophila)
Q9. Irrespective of chromosome number, a single X remains active in human somatic cells because:✓ A cell makes just enough 'blocking factor' to protect one X-inactivation centre
Q10. The Barr body is:✓ The inactive X chromosome in females
Q11. A Barr body is found in:✓ Female somatic cells
Q12. Two Barr bodies will be found in a person with the chromosome constitution:✓ AA + XXXY
Q13. The number of Barr bodies in Klinefelter syndrome (here XXYY) is:✓ 1
Q14. On amniocentesis a pregnant woman finds an extra Barr body in her embryo's cells. The likely syndrome is:✓ Klinefelter's syndrome
Q15. The XIST gene:✓ Encodes a long non-coding RNA that coats the X and helps inactivate it
Q16. The chemical basis of genomic imprinting / X-inactivation maintenance is largely:✓ Methylation of DNA
Q17. A human male carrying an allele for a trait on his single X chromosome is described as:✓ Hemizygous
Q18. Sex-linked characters are generally:✓ Recessive
Q19. Which incident is NOT associated with the Lyon hypothesis?✓ Consanguinity
Q20. Match each karyotype with its number of Barr bodies and select the correct option.✓ A-i, B-ii, C-iii, D-iv